1. Field of the Invention
This invention generally relates to a roller bearing, and, in particular, to a cross roller bearing including a plurality of rollers arranged along a predetermined path with their axes of rotation crossed between the two adjacent rollers when viewed in the direction of movement along said path.
2. Description of the Prior Art
A cross roller bearing is well known in the art. As shown in FIGS. 1 and 2, a typical cross roller bearing includes a plurality of rollers 1 arranged as being crossed along a path defined between an inner ring 2 and an outer ring 3. That is, the inner ring 2 is provided with a V-shaped groove along its outer periphery and the outer ring 3 is provided with a corresponding V-shaped groove along its inner periphery, and when the inner and outer rings 2 and 3 are put together as shown in FIG. 1, there is defined a channel having a generally square cross section. The channel defines a travelling path for the rollers 1 which are in rolling contact with the inner and outer rings 2 and 3 when set in position as shown in FIGS. 1 and 2, so that the inner and outer rings 2 and 3 are relatively rotatable through the rollers 1. Although not shown specifically, in the cross roller bearing shown in FIGS. 1 and 2, the rollers 1 are arranged such that the two adjacent rollers 1 are crossed with their axes of rotation directed perpendicular to each other when viewed in the direction of movement of the rollers 1.
In the prior art cross roller bearing, as shown in FIGS. 1 and 2, at least one of the inner and outer rings 2 and 3 (outer ring 3 in the illustrated example) was manufactured in two halves which were then put together by an appropriate fixing means, such as a bolt and nut combination. That is, in the structure illustrated in FIGS. 1 and 2, the outer ring 3 is divided into two halves 3a and 3b by a plane perpendicular to the centerline axis of the outer ring 3. Such a division of the outer ring 3 is necessary for assemblage of the bearing because the rollers 1 must be placed in position in the channel defined between the inner and outer rings 2 and 3. In the illustrated example, as best shown in FIG. 2, the top and bottom outer ring halves 3a and 3b are fixedly held together by means of a combination of bolt 4a and nut 4b, a plurality of which are typically arranged spaced apart circumferentially at equal interval.
In assembling the structure shown in FIGS. 1 and 2, for example, the bottom outer ring half 3b is first fitted onto the inner ring 2, which is unitary in structure. Then, the rollers 1 are placed in a gap defined between the inner ring 2 and the bottom outer ring half 3b such that the two adjacent rollers 1 are crossed with their axes of rotation extending perpendicular to each other when viewed in the direction of movement of the rollers 1. When the gap is filled with the rollers 1 in cross arrangement, the top outer ring half 3a is fitted onto the inner ring 2 thereby being brought into mating contact with the bottom outer ring half 3b whereby a plurality of through-holes provided in the top outer ring half 3a and spaced apart from each other circumferentially are matched to a like plurality of corresponding through-holes provided similarly in the bottom ring half 3b. Then, bolts 4a and nuts 4b are put together and tightened to complete assembling of the cross roller bearing.
The prior art cross roller bearing of the type described above suffers from various disadvantages. For example, since at least one of the inner and outer rings 2 and 3 is manufactured in two halves, it is more time consuming and expensive manufacturing such a ring of unitary structure. In addition, since the two halves are held together by a fixing means, there is a risk of loosening, which, in turn, causes a deterioration in bearing performance. Furthermore, since use must be made of a fixing means, such as the bolt and nut combination in the illustrated example, the ring which is divided into two halves must be provided with enlarged sections so as to compensate for the reduction in strength due to the provision of through-holes. In this connection, as shown in FIG. 2, that portion of the outer ring 3 which is provided with through-holes, through which the bolt 4a extends, has a local radial thickness T.sub.2 which is substantially larger than the radial thickness T.sub.1 of the inner ring 2. Thus, the prior art cross roller bearing is relatively large in size and thus heavy in weight.